fix(instance): isSoftDelete true after creating

[mirkojotic]

Pull Request check-list

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• Does npm run test or npm run test-DIALECT pass with this change (including linting)?
• Does the description below contain a link to an existing issue (Closes #[issue]) or a description of the issue you are solving?
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Description of change

Solves #10714

Handling deleted_at being undefined if not defaulted when model is created.

[codecov]

Codecov Report

Merging #10799 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #10799   +/-   ##
=======================================
  Coverage   96.33%   96.33%           
=======================================
  Files          94       94           
  Lines        9006     9006           
=======================================
  Hits         8676     8676           
  Misses        330      330

Impacted Files	Coverage Δ
lib/model.js	96.67% <100%> (ø)	⬆️

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[sushantdhiman]

🎉 This PR is included in version 5.7.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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